1. Field of the Inventions
The present inventions relate to a control unit for boats with multiple propulsion units, such as outboard motors or stern-drives (hereinafter inclusively referred to as “outboard motors”).
2. Description of the Related Art
An electric steering device for a small boat is disclosed in Japanese Patent Document JP-B-2959044. This electric steering device is designed to implement the steering action by and electric motor instead of the more traditional hydraulic mechanism. Smooth operation and accurate controllability can be obtained by such electric steering devices. This electric steering device is coupled to an outboard motor. A turning angle corresponding to the steering angle of the steering wheel is calculated by a control unit 12. Then, the electric steering device is driven according to the calculated turning angle to implement the steering action of the outboard motor.
The outboard motor in Japanese Patent Document JP-B-2959044 is connected to the steering wheel via the electric steering device, and is also connected to a remote control unit which has plural throttle levers. The remote control unit is disposed in the vicinity of the steering wheel at the operator's seat. The transmission is shifted into forward, reverse, or neutral by the operation of the throttle levers. The thrust is also controlled by tilting the throttle levers forwardly and rearward.
Generally, outboard motors provide thrust by transmitting the rotational power from the engine to a propeller via the transmission. Therefore, the minimum outboard motor thrust is generated the lowest sustainable engine speed; a speed at which the engine can run continuously without stalling.
For the trolling, for example during fishing, it is desirable to use a boat speed that is as low as possible, particularly where the operator is using the same outboard motor for both trolling and propulsion at normal cruising speed for the associated boat. However, outboard motors designed to provide achieve cruising speed operation, which can include planning speeds for smaller boats, cannot operate at a speed low enough to achieve appropriate trolling speeds. As such, operators often use separate smaller motors for trolling at appropriate trolling speeds.
FIG. 9 shows the speed relative to the throttle lever angle of the outboard motor of Japanese Patent Document JP-B-2959044.
The transmission gear is shifted into F (forward) when the throttle lever is tilted forward by the predetermined angle from the N (neutral) position. Tilting the throttle lever further forward will open the throttle gradually until it reaches the wide open throttle position. In this case, the speed v1 corresponds to the lower limit of outboard motor engine speed is attained when the transmission gear is shifted into F. In other words, the outboard motor engine cannot run at a speed below v1 without stalling. As the associated throttle lever is moved further, the speed increases up to WOT (wide open throttle) so far as the load remains constant. Thus, the lowest speed is the speed v1 corresponding to shift position F. No speed adjustment can be made in the extremely low speed range from 0 to v1 by the single outboard motor.
FIGS. 10A and 10B show a low speed control method for a boat having three outboard motors. FIG. 11 illustrates a remote control unit for controlling the three outboard motors of FIGS. 10A and 10B.
With reference to FIGS. 10A and 10B, the three outboard motors 3a, 3b, 3c are installed at the stern of a hull 1 of a small boat. A remote control unit 30 is provided in the vicinity of operator's seat (not sown) for controlling the driving of the three outboard motors 3a, 3b, 3c. The remote control unit 30 has throttle levers 31a, 31b, 31c connected to the outboard motors 3a, 3b, 3c respectively.
As shown in FIG. 11, the three throttle levers 31a, 31b, 31c can be operated independently, and are moveable from the neutral position (N) that is the vertical position at the center, to the forward shift position (F) where the throttle lever is tilted forward by the predetermined angle from the N position, and further to the wide open throttle (WOT) position where the throttle lever is tilted further forward. Also, in the reverse direction, the three throttle levers 31a, 31b, 31c are moveable from the N position to the reverse shift position (R) where the throttle lever is tilted rearward by the predetermined angle from the N position, and further to the wide open throttle (WOT) position where the throttle lever is tilted further rearward. The transmission gear shifts into forward and reverse at F position and R position, respectively. The throttle is fully closed (the lowest speed that would not cause engine stall) at each of those positions F, R. This means that the neutral position covers the range from F position to R position where the transmission gear is not engaged. Forward gear position lies in the area forward of F position, while reverse gear position lies in the area rearward of R position.
In FIG. 10(A), only the central outboard motor 3b is shifted into F (forward), while the left and right outboard motors 3a, 3c are in N (neutral) position.
In FIG. 10(B), the central outboard motor 3b is in N position, while the left and right outboard motors 3a, 3c are shifted into F.
As described above, when only part of the plural outboard motors are shifted into F with the rest of the outboard motors are kept in N, the boat speed can be reduced further from the speed at which all three outboard motors are shifted into F at the lowest speed. Also, additional speed reduction is practicable when part of the plural outboard motors are shifted into F with the rest of the outboard motors being shifted into R, and the forward thrust and the rearward thrust are adjusted by the throttle lever operation.
However, operating the three throttle levers 31a, 31b, 31c corresponding to the three outboard motors 3a, 3b, 3c is difficult in terms of correct throttle lever selection and adjustment of the tilting angle of each throttle lever. Such difficult operation makes it difficult operator to achieve smooth and comfortable operation.